Sheffield Pottery

Ultrox: Zirconium Glaze Opacifier

$5.15

Unit price: per

SKU : RMULTZIR

Item Class Raw Materials

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Product Description

A zircon opacifier for bright, clean whites at a fraction of the cost of tin. Use it wherever a recipe lists Zircopax.

You must test before you use it, at any scale. Raw materials, mined or man-made, are not consistent. Color, strength, particle size and chemistry can change from one bag to the next and from one supplier to another, even when the name on the bag stays the same. Before you use this material in a glaze, slip or clay body of any size, mix a small test batch, fire it on your own clay in your own kiln, and check the results.

What it is

An opacifier: a white powder (zirconium silicate) that turns a clear glaze into an opaque white. Zircon whites are brighter and cooler than tin whites and cost much less. Ultrox is made to substitute for Zircopax in your recipes without other changes, but test it first.

Getting started

For an opaque white, start at 8 to 10% (8 to 10 grams per 100 grams of dry glaze). Many glazes use up to 15%.
If your recipe lists Zircopax, Superpax or "zircon," use Ultrox in the same amount, then fire a test tile.
It also whitens slips and engobes and softens colors toward pastels.

For glaze formulators

Zirconium silicate, ZrSiO₄.
Stiffens the melt at higher amounts and can push glossy glazes toward satin.
Lowers glaze thermal expansion, which can help reduce crazing.
Stable with most colorants. Unlike tin, it doesn't turn pink with chrome.

Safety

Low toxicity, but don't breathe the dust. Wear a NIOSH-approved respirator (N95 or better) when handling it dry, and clean up with a wet sponge, not a broom.

Sizes & pricing

Size	Price	Per lb
1 lb	$5.15	$5.15	Add to cart
5 lb	$25.00	$5.00	Add to cart
10 lb	$49.00	$4.90	Add to cart
25 lb	$120.00	$4.80	Add to cart
55 lb bag	$247.50	$4.50	Add to cart

Full bags mix and match. Every full bag in your order, of any raw material, adds up. That total sets the price of every bag. Smaller sizes don't count.

Full bags in your order	Price per 55 lb bag	Per lb
Under 500 lb	$247.50	$4.50
500 lb and up	$243.00	$4.42
2,000 lb and up	$238.00	$4.33
6,000 lb and up	$233.00	$4.24
12,000 lb and up	$228.00	$4.15

Prices from our October 23, 2026 price list.

Frequently Asked Questions

Glaze and clay recipes go by weight, not by volume, and they don't count water. Each ingredient is a share of the dry total. 2% means 2 grams for every 100 grams of dry ingredients. For a 500-gram batch, that's 10 grams. Colors and opacifiers are often listed as extras on top of a recipe that adds up to 100, written like "+2" or "add 2%." Weigh those the same way: 2 grams for every 100 grams of the base recipe. A digital scale that reads to 0.1 gram makes small amounts easy.

A test tile is a small piece of the clay you use, glazed and fired just like your real work. Raw materials vary from bag to bag, and results also change with your clay, how thick you apply the glaze and how your kiln fires. A test tile is the only way to know what you'll get before you glaze a whole batch of pots. Write what's on each tile on the back (an underglaze pencil works), and keep notes so you can repeat what works.

Yes, whenever you handle the dry powder. Fine dust is the main hazard with most raw materials, and some can harm your lungs over time. Wear a NIOSH-approved respirator (N95 or better) while you weigh and mix. A basic dust mask that isn't N95-rated won't protect you. Once a material is mixed with water, dust is much less of a problem, but wipe up spills with a wet sponge before they dry, and mop instead of sweeping. Don't eat or drink while you work, and wash your hands afterward. Check each product's Safety section for anything extra that material needs.

Ultrox: Zirconium Glaze Opacifier

1 Pound